With respect to non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, etc., as part of performance enhancement, studies are underway to obtain higher energy densities. A higher energy density can be attained, for instance, by setting the operating voltage of positive electrode higher than a conventional one. However, when the maximum operating voltage of positive electrode is set at or above approximately 4.3 V relative to lithium metal, the high positive electrode potential is likely to cause oxidative decomposition of the electrolyte solution at the positive electrode. As a result, the durability (e.g. cycle characteristics at high temperatures) of the battery may deteriorate.
As a means to deal with such an issue, in a known technique, a fluorinated solvent (fluorine-containing solvent) is included in a non-aqueous electrolyte solution to increase the oxidation potential of the non-aqueous electrolyte solution. This means allows for inhibition of oxidative decomposition of the non-aqueous electrolyte solution at a high voltage.
As another means, Patent Document 1 teaches to coat surfaces of positive electrode active material particles with lithium-ion-conductive glass. According to Patent Document 1, this allows for inhibition of oxidative decomposition of a non-aqueous electrolyte solution at a high voltage. As a result, self-discharge characteristics may improve and battery swelling may be reduced when left standing at a high temperature.